Anthropic launches Claude Sonnet 4.5 for coding and agents

Anthropic today launched Claude Sonnet 4.5, a model focused on coding, AI agents and direct computer use. The company is presenting it as its most powerful model to date while keeping Sonnet 4 pricing at $3 per million input tokens and $15 per million output tokens.

A leap in coding that needs context

Sonnet 4.5 scores 77.2% on SWE-bench Verified, according to evaluations published by Anthropic. The benchmark uses 500 real, vetted issues from projects hosted on GitHub: the model must understand the repository, locate the problem and produce a code change that passes the relevant checks.

It is one of the most widely used indicators for comparing coding models, although it is not equivalent to a developer’s day-to-day work. A correct benchmark result alone does not measure design quality, code security, subsequent maintenance or the ability to clarify ambiguous requirements with a client.

Anthropic also says it has observed Sonnet 4.5 maintaining focus for more than 30 hours on complex, multi-step tasks. The wording matters: it does not mean that any assignment can be left running for that long without supervision. Rather, the model sustained certain long-running processes within the company’s infrastructure and testing environment.

The progress fits the broader shift in AI-assisted programming. Early copilots completed lines or generated isolated functions. Today’s tools can explore a repository, modify multiple files, run tests, consult documentation and fix their own errors. That is closer to an agent’s work than to autocomplete.

Claude gets better at using a computer

The other key figure comes from OSWorld, a benchmark that evaluates tasks performed on real computer interfaces. Sonnet 4.5 reaches 61.4%, compared with 42.2% for Sonnet 4 four months earlier. That is a 19.2-percentage-point improvement.

This capability lets Claude navigate web pages, fill out spreadsheets and interact with applications through their interfaces. Anthropic is applying it in its Claude for Chrome extension, available today to Max subscribers who joined the waitlist.

Autonomous computer use greatly expands the range of possible applications, but it also increases the risk. An agent with browser access may encounter malicious instructions hidden in a website, email or document. This is known as prompt injection: external content designed to steer the model away from its original instruction and make it disclose information or take improper actions.

Anthropic says it has strengthened its defenses against these attacks. Even so, companies will need to limit permissions, log actions and require human confirmation before sensitive operations such as sending messages, deleting files, publishing changes or making payments.

Claude Code adds restore points

The launch comes with changes to Claude Code, Anthropic’s coding tool. The main new feature is checkpoints, which save progress and let users immediately return to an earlier state if the agent introduces a problematic change.

The update also brings a redesigned terminal interface and a native Visual Studio Code extension. In the API, Anthropic is adding context editing and a memory tool so agents can manage information more effectively during long-running tasks. In the Claude apps, the model can execute code and create spreadsheets, presentations and documents within the conversation.

Checkpoints address a practical problem with coding agents: the longer they work and the more files they modify, the higher the cost of a bad decision. The ability to roll back reduces that risk, although it does not replace version control, automated testing or human review.

The Claude Code engine opens up to other developers

Anthropic has also introduced the Claude Agent SDK, a package for building agents on the same technology used in Claude Code. It includes mechanisms for managing memory, permissions and subagents that collaborate on a shared task.

The bet goes beyond selling access to a model. Anthropic wants to provide the infrastructure needed to turn it into a system capable of taking action: deciding which tool to use, retaining relevant information and dividing work among multiple processes. The SDK is not limited to coding and could be applied, for example, to document analysis, research or internal business automation.

For developers, Sonnet 4.5 is available today through the API under the identifier claude-sonnet-4-5. Keeping Sonnet 4 pricing makes it easier to replace the previous model without raising the per-token cost, although the total expense will depend on how many steps, tool calls and retries each agent requires.

More capability, but also stronger safety measures

Sonnet 4.5 is being deployed under Anthropic’s AI Safety Level 3 protections. This internal level requires additional safeguards against capabilities that could increase risks related to chemical, biological, radiological or nuclear weapons.

Those measures include classifiers that examine potentially dangerous inputs and outputs. Anthropic acknowledges that these filters may block legitimate content and allows certain conversations to continue with Sonnet 4, which it considers lower-risk in this area. The company says it has reduced false positives tenfold since it first described the system and by half since the launch of Claude Opus 4 in May.

The company also reports improvements against behaviors such as excessive user flattery, deception, power-seeking and reinforcement of delusional ideas. These are results from the company’s own evaluations, documented in the model’s safety card; experience with real-world deployments will show how they translate to conversations and agents with tool access.

Sonnet 4.5 thus strengthens its position in generative AI’s most hotly contested commercial arena: systems that do more than respond, modifying code and operating applications. For businesses, the decision will no longer depend solely on which model scores highest on a benchmark, but on how much work it completes per euro, what errors it makes and what controls it provides when acting on real systems.